Watching bread yeast make bubbles

Marmite is in fact yeast extract, which is made by adding salt to a yeast suspension, but the process of manufacture is secret.

Materials

• Bowl
• Warm water
• Active dry bread yeast
• Sugar
• Balloon
• Bottle
• Tooth Pick
• Glass microscope slide
• Plastic cover slips

See information on suppliers here.

Methods

1. Put a pack of yeast in a bowl.
2. Add warm water and 2 tablespoons sugar and mix with a spoon.
3. Transfer the mixture into a bottle.
4. Place a balloon around the bottle neck and wait approx. 10min, during which time the balloon should inflate due to the released carbon dioxide gas.

Wine is made by fermentation of the sugars in the grapes by yeasts that live on them.

To observe the yeast under the microscope:

1. Place a drop of the yeast mixture on the microscope slide (it might be necessary to dilute it a bit more with water).
2. Place a coverslip on top and observe under different magnifications. High magnifications will be needed to see the yeast well.

Yeasts are microscopic unicellular fungi that are used to make bread, beer and wine by fermentation. Yeasts reproduce by budding (asexual reproduction), when a small bud forms and splits to form a new daughter cell, but under stress conditions they can produce spores (a form of sexual reproduction). The bread yeast Saccharomyces cerevisiae uses the sugars in the flour to produce energy, releasing the alcohol ethanol (which evaporates) and bubbles of the gas carbon dioxide, which makes the bread dough rise. The bread yeast is also used to make some types of beer; in this case the yeast uses the sugars from cereals like barley, to produce ethanol and carbon dioxide. The bread yeast has been widely used by scientists to study important cellular processes.